The invention relates to cosmetic and pharmaceutical formulations. More specifically, the invention relates to cosmetic and pharmaceutical formulations containing low levels of emulsifiers.
One of the most common vehicles for cosmetic and pharmaceutical products is the emulsion. Because they are formed by the dispersion of an oil in water, or water in an oil, they provide great versatility in the delivery of different types of active ingredients. A single oil and water formulation can be used to deliver both oil soluble and water soluble active components, thereby giving the formulation a range of potential activity that cannot be matched by a single phase system.
There are of course limitations to an emulsion vehicle, by virtue of its combination of two inherently incompatible phases. First, an emulsion ordinarily will have a certain amount of innate viscosity; while not necessarily a problem per se, the thickness of the emulsion can prevent its use in certain types of products or packaging that require a less viscous texture. In addition, in order to maintain a stable dispersion, it is ordinarily necessary to add to the formulations substantial amounts of emulsion stabilizers and/or emulsifiers. The necessity of addition of these materials not only adds cost to the final product, but also has an effect on the quality of the final product, by affecting the way the emulsion breaks, as well as how it feels on the skin. Added stabilizers can add to the viscosity of the emulsion, and certain emulsifiers can be irritating to the skin of some users.
There have been attempts to overcome some of these difficulties. One common approach is the use of high pressure homogenization techniques, in which a crude emulsion is passed through a high pressure homogenizer to yield a relatively thin emulsion. This technique can contribute to a reduction in the viscosity of the emulsion, and such emulsions have even been stated as being made with relatively low levels of emulsifiers. However, the emulsifiers used in these situations are either of the type that are known to cause irritation, i.e., non-ionic ethoxylated emulsifiers, or amphoteric, lecithin-type (phospholipid) emulsifiers, which, being naturally-occurring products, are rather costly to use. In some cases, these emulsions will still require an addition of emulsion stabilizers to maintain stability over long periods of time. There thus continues to be a need for a water-thin emulsion which employs minimal levels of a non-irritating emulsifier.
The present invention relates to water-thin emulsions prepared by high pressure homogenization, in the presence of a non-phospholipid, non-ethoxylated xe2x80x9cpseudoemulsifierxe2x80x9d having a chemical composition comprising at least one hydrophobic moiety, and at least one polar moiety, the size and/or the planar arrangement of the hydrophobic and polar moieties being asymmetrical with respect to each other. Preferably, the pseudoemulsifier contains at least two of one or of both of the types of moieties. Although not ordinarily effective for use alone in maintaining stability of emulsions, the pseudoemulsifiers have been shown to be highly effective in maintaining the stability of these water-thin emulsion, even at very low levels, i.e., less than 1%, and in addition are very mild and non-irritating to the skin. The water-thin emulsions find a variety of uses as a base for both cosmetic and pharmaceutical products. The invention also provides a method for producing a water-thin emulsion, comprising mixing oil and water phases in the presence of the pseudoemulsifier, and subjecting the mixture to high pressure homogenization.